New Diagnostic Tools for Improving Fertilizer Management

In crop production, improving plant health and soil fertility is key to maximizing yield and profitability. A better understanding of how soil organisms can benefit nutrient uptake and improve efficiency can help farm managers optimize fertilizers and nutrient applications. This in turn can help reduce environmental impacts and greenhouse gas emissions, while improving carbon sequestration and profitability.

“Arbuscular mycorrhizal fungi (AMF) are soil organisms that are naturally present in most cultivated soils of Canada,” explains Dr. Chantal Hamel, Research Scientist with Agriculture and Agri-Food Canada (AAFC) in Swift Current, Saskatchewan. “We can think of them as probiotics for plants because they help improve plant health in many ways. The AMF form a dense network connected inside and outside of plant roots that can rapidly transport soil nutrients into the plants, which is particularly important for nutrients like phosphorus, copper and zinc that are not very mobile in the soil.” AMF are also known to protect plants against abiotic stress (heat, drought, cold, salinity) and soil-borne pathogens, such as Fusarium and Pythium species.

There are many AMF species in soils, but only a dozen species are dominant in agricultural fields from the Rockies to the Atlantic. AMF are biotrophic, which means they require living plants to complete their lifecycle. Therefore, the type of mycorrhizae available in soils will depend on the plants grown in the field. “AMF fungi form preferential associations with plants. Periods of monoculture may reduce the diversity of AMF. Also, some plants such as canola or mustard do not form symbiosis,” explains Hamel. “After a crop year of canola or mustard, or a year of fallow, there will be a reduced population of these fungi in the soil.”

The establishment of symbiosis of plants and AMF is similar to nitrogen (N) fixation in legumes. “If N is applied to a pea crop for example, the plants will not bother fixing their own N,” explains Hamel. “Similarly, if there is too much P in the soil, then the plant will not form symbiosis with the AMF and the benefits of nutrient uptake and disease suppression by AMF are lost. Since excess P will build up rather than be washed out or lost as gas like it happens with N, it is very important to develop a system so that we can adjust the fertility of the soil more appropriately and keep the benefits of symbiosis.”

New Diagnostic Tools and Crop Models

Until recently, it has been difficult to determine the relative abundance and distribution of AMF in farmers field. Recent advances and new techniques for soil microbiology research are helping researchers develop innovative diagnostic tools and crop models to improve effective management of these important beneficial fungi in crop production.

“We have developed two innovative approaches to determine the relative abundance and distribution of AMF in farmers fields,” explains Hamel. “DNA sequencing techniques initially helped us with identification and distribution of AMF, but we needed other approaches to really understand the abundance and how that might impact crop production. The first approach is a direct measurement of AMF using a DNA probe, which is a very good and useful approach but can be expensive. The second approach is based on computer models, similar to weather forecasting, using regular soil test data from a standard soil test.”

Hamel and her team have partnered with Western Ag Innovations in Saskatoon to develop a forecasting model for wheat. “The abundance and distribution of AMF can be estimated from a standard soil test and a GPS location using a computer model,” explains Hamel. “Using all of the current information that is available for making fertilizer recommendations, this model can now add in information about the abundance of AMF and the capacity of the soil to supply nutrients to the crop. This method doesn’t require any additional testing, all of the information is available in the standard soil test data and national soil and climate databases.”

The final details are being completed on the forecasting model for wheat, and Hamel is hoping to receive additional funding over the next few years to expand the development of forecasting models for other crops. “For now the information we have available is restricted to the Prairie soil zones in Canada and the northern US,” says Hamel. “However, in Canada about 80% of the agriculture land is in this area, so the computer model is useful over a large number of acres. We expect these tools to be available for the 2013 crop production season.”

Ultimately the tools and models will provide farmers with better information for adjusting fertilizer recommendations and keeping the benefits of symbiosis. Hamel believes these new tools and models, in conjunction with the development of improved inoculants and signal molecules to manipulate AMF and the development of cultivars with improved symbiotic qualities, will enable farmers to build the resource base of their land and improve crop yield stability, while improving agroecosystems’ sustainability and resilience.